feat(crypto-tail): 策略最小价差(无/固定/自动) + 前端默认与文案

- 后端: 最小价差 DB/Entity/DTO、Binance K线 REST+WS、自动价差 IQR 预计算与执行时校验
- 前端: 最小价差(自动-固定-无)，默认自动，label 旁 info 说明，选择自动不展示建议约
- i18n: minSpreadModeTip 说明不写死标的
- 文档: crypto-tail-strategy-min-spread-flow.md
- scripts: Binance K线拉取与 WS 示例

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/services/api.ts

@@ -447,6 +447,8 @@ export const apiService = {
       maxPrice?: string
       amountMode: string
       amountValue: string
+      minSpreadMode?: string
+      minSpreadValue?: string | null
       enabled?: boolean
     }) =>
       apiClient.post<ApiResponse<import('../types').CryptoTailStrategyDto>>('/crypto-tail-strategy/create', data),
@@ -459,6 +461,8 @@ export const apiService = {
       maxPrice?: string
       amountMode?: string
       amountValue?: string
+      minSpreadMode?: string
+      minSpreadValue?: string | null
       enabled?: boolean
     }) =>
       apiClient.post<ApiResponse<import('../types').CryptoTailStrategyDto>>('/crypto-tail-strategy/update', data),
@@ -467,7 +471,9 @@ export const apiService = {
     triggers: (data: { strategyId: number; page?: number; pageSize?: number; status?: string }) =>
       apiClient.post<ApiResponse<{ list: import('../types').CryptoTailStrategyTriggerDto[]; total: number }>>('/crypto-tail-strategy/triggers', data),
     marketOptions: () =>
-      apiClient.post<ApiResponse<import('../types').CryptoTailMarketOptionDto[]>>('/crypto-tail-strategy/market-options', {})
+      apiClient.post<ApiResponse<import('../types').CryptoTailMarketOptionDto[]>>('/crypto-tail-strategy/market-options', {}),
+    autoMinSpread: (data: { intervalSeconds: number }) =>
+      apiClient.post<ApiResponse<import('../types').CryptoTailAutoMinSpreadResponse>>('/crypto-tail-strategy/auto-min-spread', data)
   },
   
   /**